A negotiated solution to the crisis in Ivory Coast looks increasingly out of reach as armed forces allied to Alassane Ouattara, the internationally recognised winner of November’s presidential election, press on with an offensive that has seen several towns in the west of the country fall in recent days and fighting break out in the east.

According to the UN refugee agency, as many as 1m people have fled the commercial capital Abidjan, where guerrillas opposed to Laurent Gbagbo, the outgoing president, calling themselves “invisible commandos”, have seized control of northern neighbourhoods that are populated mostly by sympathisers of the president-elect.

Though Mr Gbagbo’s government has been squeezed by international sanctions and cut off from the regional central bank which controls its currency, the populist incumbent remains stubbornly in place.

He has refused to concede defeat or dance to the tune of an African Union mediation panel that has recognised Mr Ouattara’s victory, and called for the formation of a coalition government under his control.

Months of gridlock have steadily given way to conflict, with the official death toll from related violence climbing towards 500. The UN is investigating reports that a further 200, mostly West African migrants, have been killed.

Ivory Coast was once viewed as the cosmopolitan heart of French-speaking west Africa, and its descent into anarchy has the potential to destabilise much of the region.

Reuters news agency reported on Tuesday that former rebels allied to Mr Ouattara who have controlled northern Ivory coast since a 2002-03 civil war, had seized the town of Daloa at the heart of the country’s cocoa industry. There were also reports of heavy fighting around Duekoue, further to the west.

The area, which produces about half the country’s annual crop of 1.2m tonnes of cocoa, the world's largest, is now under the control of pro-Ouattara forces, potentially opening up a route to the port of San Pedro on the Atlantic coast.

Regional diplomats said Mr Gbagbo had been offered refuge in both South Africa and Angola, two states that have been sympathetic to his claims of being cheated of election victory and the victim of a neo-imperialist conspiracy led by France.

But the former history lecturer appears unlikely to cede power willingly to Mr Ouattara, and has been able to continue paying the army and much of the civil service.